A human vertebra has a rearwardly projecting portion known as a spinous process. Bending of the spine can cause the spinous processes of adjacent vertebrae to move toward each other. This may, in some people, constrict the space in the spinal canal and foramina and, thus, may cause pain. Such constriction, which is known as stenosis, can be treated by the implantation of an interspinous spacer into the space between adjacent spinous processes.
Current interspinous spacers are typically constructed of separate pieces which require insertion from opposite sides of the spine, in a posterior approach, and necessitate rather large incisions, cutting both left and right thoracolumbar fascia as well as stripping the multifidus muscles from their attachments.
It is desirable to provide an interspinous spacer for implantation between spinous processes of adjacent vertebrae which can be laterally inserted in a first configuration through a single opening in a minimally invasive approach and which may then be deployed to a second configuration to maintain the spacer in position between the adjacent spinous processes.
In addition, current interspinous spacers are typically constructed from a metallic material such as, for example, titanium or a titanium alloy, or a polymer. However, in some cases of fractured or otherwise damaged bones, bone grafts may be used to repair or otherwise treat a damaged area. In the United States alone, approximately half a million bone grafting procedures are performed annually, directed to a diverse array of medical interventions for complications such as fractures involving bone loss, injuries or other conditions necessitating immobilization by fusion (such as for the spine or joints), and other bone defects that may be present due to trauma, infection, or disease. Bone grafting involves the surgical transplantation of pieces of bone within the body, and generally is effectuated through the use of graft material acquired from a human source. Human graft material is primarily utilized due to the limited applicability of xenografts, e.g., transplants from another species.
Some orthopedic procedures involve the use of allografts, which are bone grafts from other human sources (normally cadavers). Allografts, for example, are placed in a host bone and serve as the substructure for supporting new bone tissue growth from the host bone.
Manufacturing a bone-derived spacer however has its difficulties. For example, the various bones of the human body such as the femur (thigh), tibia and fibula (leg), humerus (upper arm), radius and ulna (lower arm) have geometries that vary considerably. The lengths of these bones are varied, as well as the shape of the cross section of each type of bone and the shape of any given bone over its length. In addition, the wall thickness may vary in different areas of the cross-section of each bone. Thus, the use of any given bone to produce a spacer or a component of a spacer may be a function of the donor bone's dimensions and geometry. Machining of bones, however, may permit the production of a spacer or a component of a spacer with standardized or custom dimensions.
Thus, it is desirable to provide a safe and effective interspinous spacer that can be manufactured from bone, laterally insertable via a minimally invasive surgical technique and once positioned, deployable to maintain the interspinous spacer in position.